U.S. patent number 10,760,003 [Application Number 16/127,901] was granted by the patent office on 2020-09-01 for process and apparatus for treating waste comprising mixed plastic waste.
This patent grant is currently assigned to Recycling Technologies LTD. The grantee listed for this patent is Recycling Technologies LTD. Invention is credited to Adrian Edward Griffiths.
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United States Patent |
10,760,003 |
Griffiths |
September 1, 2020 |
Process and apparatus for treating waste comprising mixed plastic
waste
Abstract
A process for treating waste comprising Mixed Plastic Waste is
disclosed. The process comprises includes feeding the waste to a
pyrolysis reactor, pyrolysing the waste in the pyrolysis reactor to
produce a fuel and using the fuel to run a generator to produce
electricity.
Inventors: |
Griffiths; Adrian Edward
(Swindon, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Recycling Technologies LTD |
Swindon |
N/A |
GB |
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Assignee: |
Recycling Technologies LTD
(Swindon, GB)
|
Family
ID: |
48048703 |
Appl.
No.: |
16/127,901 |
Filed: |
September 11, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190016960 A1 |
Jan 17, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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16124608 |
Sep 7, 2018 |
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14768066 |
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10093860 |
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PCT/GB2013/052849 |
Oct 31, 2013 |
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Foreign Application Priority Data
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Feb 20, 2013 [GB] |
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1303005.1 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G
31/09 (20130101); C10G 1/10 (20130101); C10B
53/07 (20130101); B01J 8/44 (20130101); C10B
49/10 (20130101); C10K 1/024 (20130101); F02B
43/08 (20130101); C10G 1/002 (20130101); B01J
8/1818 (20130101); Y02P 20/143 (20151101); Y02T
10/30 (20130101) |
Current International
Class: |
C10B
53/07 (20060101); C10K 1/02 (20060101); F02B
43/08 (20060101); C10G 1/10 (20060101); B01J
8/44 (20060101); C10B 49/10 (20060101); C10G
31/09 (20060101); C10G 1/00 (20060101); B01J
8/18 (20060101) |
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Other References
Sinn, H., et al., "Processing of Plastic Waste and Scrap Tires into
Chemical Raw Materials, Especially by Pyrolysis", 1976, 13 pgs.
cited by applicant .
The Origin and Chemistry of Petroleum. (2001). Chemical
Constituents of Petroleum and Its Refined Products. Pace
Analytical. Fig. A-1. Accessed Aug. 15, 2017 at
https://www.pacelabs.com/environmental-services/energy-services-forensics-
/forensics-101-a-primer/the-origin-and-chemistry-of-petroleum.html.
cited by applicant .
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cited by applicant .
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|
Primary Examiner: Miller; Jonathan
Assistant Examiner: Gitman; Gabriel E
Attorney, Agent or Firm: Bondi; Michael A. Moss &
Barnett
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
This application is a Continuation of U.S. application Ser. No.
16/124,608, filed Sep. 7, 2018, which claims priority to U.S.
application Ser. No. 14/768,066, filed on Aug. 14, 2015, which
claims priority to PCT Applic. No. PCT/GB2013/052849, filed on Oct.
31, 2013, which claims priority to U.K. Applic. No. 1303005.1,
filed on Feb. 20, 2013, the contents of which are incorporated
herein by reference.
Claims
The invention claimed is:
1. A portable apparatus for treating waste comprising mixed plastic
waste, wherein the apparatus comprises: a pyrolysis reactor for
pyrolysing the waste to produce a pyrolysis product, wherein the
pyrolysis reactor is a fluidised bed reactor configured to contain
a fluidised bed of particles; a distributor mounted in the
pyrolysis reactor, wherein the distributor is configured to feed a
fluidisation medium into the fluidised bed, wherein the distributor
comprises an array of ducts arranged in a horizontal grid and
spaced apart such that, in use, a portion of the particles can fall
through the distributor between the ducts; a cleaning system that
is capable of cleaning and reheating the particles; a condenser
that is capable of condensing the pyrolysis product to form a
liquid fraction and a gas fraction; and at least one tank that is
capable of storing the liquid fraction as a liquid, a solid, or a
mixture of a liquid and a solid; wherein the pyrolysis reactor
comprises: a particle inlet provided in the pyrolysis reactor above
the distributor, wherein the particle inlet is configured to
receive the cleaned and reheated particles from the cleaning system
and feed the cleaned and reheated particles into the fluidised bed;
and a particle outlet provided in the pyrolysis reactor below the
distributor, wherein the particle outlet is configured to receive
the portion of the particles that have fallen through the
distributor and transfer the portion of particles to the cleaning
system; wherein the pyrolysis reactor is mounted in a first frame
having fittings that are compatible with load handling equipment
used to transport freight containers and wherein the first frame is
compatible with the ISO standards for freight containers, and
wherein the apparatus is sized and configured to treat from 5,000
to 20,000 tonnes per year of waste.
2. The portable waste treating apparatus according to claim 1,
wherein the at least one tank is mounted in a second frame having
fittings that are compatible with load handling equipment used to
transport freight containers and wherein the at least one tank is
connectable to the condenser to form the apparatus for treating
waste.
3. The portable waste treating apparatus according to claim 1,
wherein the first frame is an ISO compatible intermodal container
frame.
4. The portable waste treating apparatus according to claim 1,
wherein the condenser is mounted in a second frame having fittings
that are compatible with load handling equipment used to transport
freight containers, and wherein the condenser is connectable to the
pyrolysis reactor to form the apparatus for treating waste.
5. The portable waste treating apparatus according to claim 1,
wherein the apparatus comprises at least one component selected
from the list consisting of: a storage vessel upstream of the
pyrolysis reactor for storing the waste prior to feeding the waste
to the pyrolysis reactor, wherein the storage vessel comprises a
blending system for blending the waste stored in the vessel; a
dryer upstream of the pyrolysis reactor for drying the waste; a hot
gas filter system for filtering the pyrolysis product to remove
chemical contaminants; a combustor to combust a product from the
pyrolysis reactor to heat a fluid that is fed into the pyrolysis
reactor to heat the pyrolysis reactor; and, a generator configured
to run on the liquid fraction to produce electricity; wherein the
at least one component is mounted in a second frame having fittings
that are compatible with load handling equipment used to transport
freight containers.
6. The portable waste treating apparatus according to claim 5,
wherein the second frame is separate from the first frame, and
wherein the at least one component is connectable to another
component, the pyrolysis reactor, the condenser or the at least one
tank to form the apparatus for treating waste.
7. The portable waste treating apparatus according to claim 5,
wherein the apparatus comprises at least two components selected
from said list, and wherein the at least two components are mounted
in the second frame.
8. The portable waste treating apparatus according to claim 5,
wherein the apparatus comprises at least two components selected
from said list, and wherein the at least two components are mounted
in separate frames.
9. The portable waste treating apparatus according to claim 8,
wherein the separate frames of the at least two components are
separate from the first frame, and wherein each of the at least two
components is connectable to another component, the pyrolysis
reactor, the condenser or the at least one tank to form the
apparatus for treating waste.
10. The portable waste treating apparatus according to claim 9,
wherein each frame is an ISO compatible intermodal container
frame.
11. The portable waste treating apparatus according to claim 5,
wherein the apparatus comprises at least four components selected
from said list, wherein the at least four components are mounted in
separate frames, and wherein each of the at least four components
are connectable to another component, the pyrolysis reactor, the
condenser or the at least one tank to form the apparatus for
treating waste.
12. The portable waste treating apparatus according to claim 1,
wherein the apparatus is sized and configured to treat from 5,000
to 10,000 tonnes per year of waste.
13. The portable waste treating apparatus according to claim 1,
wherein the distributor ducts have orifices in their respective
surfaces, wherein the ducts in the array are spaced apart such
that, in use, the particles can fall between the ducts.
14. The apparatus according to claim 1, wherein the fluidised bed
of the fluidised bed pyrolysis reactor has at least one of 1) a
mass of 2.5 to 3.5 tonnes, and 2) an aspect ratio (height:width) of
about 1:1.
15. The apparatus according to claim 1, wherein the fluidised bed
pyrolysis reactor is sized and configured to treat about 1,000 kg
of waste per hour.
16. A method of constructing an apparatus for treating waste
comprising mixed plastic waste, wherein the apparatus comprises a
fluidised bed pyrolysis reactor for pyrolysing the waste to produce
a pyrolysis product and configured to contain a fluidised bed of
particles, a cleaning system for cleaning and reheating particles
of the fluidised bed, a condenser for condensing the pyrolysis
product to form a liquid fraction and a gas fraction, and at least
one tank for storing the liquid fraction as a liquid, a solid, or a
mixture of a liquid and a solid; a distributor configured to feed a
fluidisation medium into the fluidised bed of particles, wherein
the distributor comprises an array of ducts arranged in a
horizontal grid and spaced apart such that, in use, the particles
can fall through the distributor between the ducts; an outlet below
the distributor through which a portion of the particles that have
fallen through the distributor are removed and transferred to the
cleaning system; and an inlet above the distributor through which
cleaned and reheated particles are fed back into the fluidised bed
from the cleaning system; wherein the apparatus is sized and
configured to treat from 5,000 to 20,000 tonnes per year of waste;
and wherein the method comprises: constructing a pyrolysis reactor
module at a manufacturing location, wherein the pyrolysis reactor
module comprises the fluidised bed pyrolysis reactor mounted in a
frame having fittings that are compatible with load handling
equipment used to transport freight containers and wherein the
frame is compatible with the ISO standards for freight containers;
transporting the pyrolysis reactor module to an installation
location; and connecting the pyrolysis reactor module to another
module to form the apparatus.
17. The method according to claim 16, wherein the frame of the
pyrolysis reactor module is an ISO compatible intermodal container
frame.
18. The method according to claim 16, wherein the method comprises
constructing a condenser module at a manufacturing location,
transporting the condenser module to the installation location, and
connecting the condenser module to the pyrolysis reactor module to
form the apparatus; wherein the condenser module comprises a
condenser mounted in a frame having fittings that are compatible
with load handling equipment used to transport freight
containers.
19. The method according to claim 16, wherein the method comprises
constructing at least one other module at a manufacturing location,
transporting the at least one other module to the installation
location, and connecting the at least one other module to another
module or the pyrolysis reactor module to form the apparatus;
wherein the at least one other module is selected from the list
consisting of: a storage vessel module comprising a storage vessel
having a blending system for storing and blending the waste; a
dryer module comprising a dryer for drying the waste; a filter
system module comprising a filter system for filtering the
pyrolysis product to remove chemical contaminants; a combustor
module comprising a combustor for combusting a product from the
pyrolysis reactor to heat a fluid that is fed into the pyrolysis
reactor to heat the pyrolysis reactor; and, a generator module
comprising a generator configured to run on the liquid fraction to
produce electricity; and wherein, the at least one other module
comprises a frame having fittings that are compatible with load
handling equipment used to transport freight containers.
20. The method according to claim 19, wherein the method comprises
constructing, transporting and connecting at least two of said
modules, and wherein the at least two modules share a single
frame.
21. The method according to claim 19, wherein the method comprises
constructing, transporting and connecting at least two of said
modules, and wherein the at least two modules have separate
frames.
22. The method according to claim 19, wherein the method comprises
constructing, transporting and connecting at least four of said
modules, and wherein the at least four modules have separate
frames.
23. The method according to claim 19, wherein the manufacturing
location for construction of the pyrolysis reactor is the same as
the manufacturing location for the at least one other module.
24. The method according to claim 16, wherein the apparatus is
sized and configured to treat from 5,000 to 10,000 tonnes per year
of waste.
25. The method according to claim 19, wherein the method comprises:
disconnecting the pyrolysis reactor from the at least one other
module; transporting the pyrolysis reactor module to a second
location; transporting the at least one other module to the second
location; and, reconnecting the pyrolysis reactor module to the at
least one other module to re-form the apparatus.
26. The method according to claim 16, wherein the installation
location is on a ship.
27. The method according to claim 17, wherein the fluidised bed of
the fluidised bed pyrolysis reactor has at least one of 1) a mass
of 2.5 to 3.5 tonnes, and 2) an aspect ratio (height:width) of
about 1:1.
28. The method according to claim 17, wherein the fluidised bed
pyrolysis reactor is sized and configured to treat about 1,000 kg
of waste per hour.
Description
FIELD OF THE INVENTION
The present invention concerns processes and apparatus for the
treatment of waste comprising Mixed Plastic Waste.
BACKGROUND OF THE INVENTION
In many countries, waste material is collected and taken to
processing centres or recycling centres. Some categories of waste
are separated out and sent to recycling processes, either at the
centre or elsewhere. For example, waste glass is commonly recycled.
Waste that is not recycled may be sent to landfill or may be burnt,
typically to provide either heat or electrical energy.
Large amounts of plastic are used in modern goods and packaging and
there is therefore a large quantity of plastic waste, typically
termed Mixed Plastic Waste, passing through recycling centres.
Typically, PET and HDPE are separated out for recycling and the
remainder is sent to landfill. However, landfill may not be a
popular option and there therefore exists a need to find other ways
of dealing with Mixed Plastic Waste, either on its own or combined
with organic material as Municipal Solid Waste.
Some solutions have been proposed for Mixed Plastic Waste. For
example, Mixed Plastic Waste may be used as a fuel in a power
station. However, the cost of electricity generated in such a way
may be ten times the cost of electricity generated from a
conventional fossil fuel, such as natural gas. It may also be
difficult to use all the heat produced in such processes and much
of it is therefore dissipated in cooling towers. The combination of
low efficiency and high capital cost can make such solutions
unattractive.
Pyrolysis of Mixed Plastic waste has been suggested as a solution.
Examples include the use of pyrolysis to create fuel for vehicles,
combining pyrolysis with plasma treatment to produce hydrogen and
pyrolysis for disposal of plastic waste at sea. However, such
processes may suffer from drawbacks, including the difficulty of
producing a uniform, high-quality product from a highly variable
feed such as waste and the difficulty of effectively using all the
pyrolysis products.
The present invention seeks to mitigate the above-mentioned
problems. Alternatively or additionally, the present invention
seeks to provide an improved process and apparatus for the
treatment of waste comprising Mixed Plastic Waste.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a
process for treating waste comprising Mixed Plastic Waste, the
process comprising: feeding the waste to a pyrolysis reactor;
pyrolysing the waste in the pyrolysis reactor to produce a fuel;
and using the fuel to run a generator to produce electricity.
By pyrolysing the waste, it is possible to create a fuel that
powers a standard engine, for example a marine diesel engine
attached to a generator. Such a process may be advantageous in that
the capital cost of setting up such a process may be lower than for
a bespoke combustion process.
Mixed Plastic Waste will be understood to be a mixture of waste
plastics. That mixture of plastics could originate from separate
streams of plastics or could originate from a single stream of
comingled plastics. In many cases, Mixed Plastic Waste will result
from domestic refuse, such as that traditionally collected in black
bags in the UK. Such `black bag waste`, or Municipal Solid Waste,
will comprise Mixed Plastic Waste. It may be that the Municipal
Solid Waste is fed to the process, but advantageously some
separation occurs to remove waste, such as glass and certain
plastics, such as HDPE and PET, that can be recycled before feeding
the waste to the process. The separations that occur may depend on
what other facilities are available to recycle or otherwise use
parts of the incoming waste to the facility. Thus, at some
facilities, the waste fed to the process may be Municipal Solid
Waste. At some facilities the waste fed to the process may be Mixed
Plastic Waste. At some facilities the waste fed to the process may
comprise greater than 10 wt % Mixed Plastic Waste or greater than
20 wt % Mixed Plastic Waste. Preferably the waste fed to the
process comprises greater than 30 wt % Mixed Plastic Waste, more
preferably greater than 40 wt % Mixed Plastic Waste, more
preferably greater than 50 wt % Mixed Plastic Waste, more
preferably greater than 60 wt % Mixed Plastic Waste, more
preferably greater than 70 wt % Mixed Plastic Waste, more
preferably greater than 80 wt % Mixed Plastic Waste and more
preferably greater than 90 wt % Mixed Plastic Waste. It will be
appreciated that waste comprising a high percentage of Mixed
Plastic Waste may be advantageous because of a high energy density
and also because such waste may be difficult to treat in other ways
and may typically be sent to landfill. It may be that the waste
further comprises organic waste. Advantageously the waste may
contain greater than 70 wt % organic waste. Such waste may count as
biomass for the purpose of government schemes such as the Renewable
Obligations Certificate scheme in the UK. In such cases, the waste
preferably comprises greater than 5 wt %, more preferably greater
than 10 wt %, even more preferably greater than 20 wt % and still
more preferably greater than 25 wt % Mixed Plastic Waste.
Advantageously the waste composition is such that there is
sufficient organic waste to qualify as biomass but that
substantially the remainder of the waste is Mixed Plastic Waste so
as to increase the energy density.
Preferably the process comprises passing the fuel through a
condenser to form a liquid fraction and a gas fraction and using
the liquid fraction of the fuel to run the generator. Using liquid
fuel in the generator is preferable from a cost and simplicity
point of view. Liquid fuels may be easier to store and handle and
may be used in a wide variety of generators.
Preferably the process comprises storing the fuel in a buffer tank
prior to using it to run the generator. The buffer tank is, for
example, a tank in which the level of the fuel can vary. In that
way, variations in the rate at which the fuel is produced and
consumed can be accommodated by allowing the reserve of fuel stored
in the buffer tank to increase or decrease. That may be
particularly advantageous in a process such as the present
invention, as it may be most efficient to run the pyrolysis reactor
at a constant rate so as to achieve a steady operating state, but
the demand for electricity varies through the day. Thus the
quantity of fuel in the buffer tank is allowed to increase at times
of low electricity demand and to decrease at times of high
electricity demand. For example, it may be that the fuel is
produced continuously and the generator is run intermittently. It
will be appreciated that continuous production means that the
process for producing the fuel is run continuously over an extended
period of time such as days, weeks or months.
It may be that the process includes mixing the fuel while it is in
the buffer tank. For example, some of the fuel may be drawn from
one part of the tank and recirculated to a different part of the
tank. If the buffer tank comprises multiple tanks, the mixing may
be achieved by circulating the fuel between the tanks. Mixing the
fuel in the buffer tank may smooth out fluctuations in the
properties of the fuel that result from variability in the waste
fed to the process. That may provide a more uniform heat of
combustion of the fuel over time and may also prevent emissions
spikes resulting from short-term rises in contamination in the
waste feed.
Preferably, the fuel is stored as a liquid and/or as a solid. The
fuel may thus be stored as a liquid, a solid, or a mixture of a
liquid and a solid. It will be appreciated that heavy fuels, such
as bunker fuel commonly used in shipping, may be solid, or a
mixture of tarry liquids and solids, at ambient temperatures and
become liquid when warmed, for example to around 50.degree. C. Thus
such fuels may be stored as a liquid, or a solid or a mixture of a
liquid and solid depending on temperature. It will be appreciated
that the tank volume required for liquid/solid storage may be
significantly smaller than for storing an equivalent amount of fuel
(in energy terms) as a gas. Liquid/solid storage may also be
intrinsically safer. The process may comprise warming the fuel in
the buffer tank so as to transfer, for example pump, it to the
generator. The warming may be achieved using heat from the
generator, when it is running, or by using an external source of
heat, for example at start up.
The buffer tank may comprise a tank container, for example a tank
container compatible with ISO standards for intermodal tank
containers. Preferably the buffer tank comprises a so-called "20
ft" tank container. Thus the buffer tank may be 6.1 m long and 2.44
m wide and high and mounted in an ISO compatible intermodal
container frame. The volume of the tank may be from 14,000 to
27,000 litres. In some embodiments the buffer tank may comprise a
plurality of tank containers. Such an arrangement may be
advantageous in that a plurality of container tanks may be simpler
and cheaper to manufacture and deliver than a single large tank and
in that capacity may be straightforwardly added by providing
further container tanks. Multiple container tanks may also provide
for flexibility in maintenance and operation and be safer than a
single large tank.
Preferably the process comprises filtering the fuel to remove
chemical contaminants. Emissions from generators may be subject to
strict controls and it is possible that fuel produced from waste
may contain significant levels of chemical contamination. For
example, PVC in the plastic waste may mean that there are
undesirable levels of chlorine in the fuel as it exits the
pyrolysis reactor. Other chemical contaminants include fluorine and
sulphur. By filtering the fuel, the chemical contamination can be
removed before the fuel is used in the generator. The filtering may
therefore remove chemicals associated with poor emissions, for
example emissions that would contravene the Waste Incineration
Directive. The fuel may be filtered in the gas phase. That is, the
fuel may exit the pyrolysis reactor as a gas and be filtered in the
gas phase before the fuel is condensed. It will be appreciated that
the fuel is filtered before it is used in the generator. Thus the
filtration occurs before combustion. There may be a significant
advantage in filtering the fuel after the pyrolysis but before it
is used in the generator. Pyrolysis breaks down the chain lengths
of the hydrocarbons in the plastics, resulting in smaller
molecules. Combustion, on the other hand combines the hydrocarbons
with oxygen, typically from air, which results in a large volume of
exhaust gas. The result is that the volume of fuel gas exiting the
pyrolysis reactor may be significantly lower than the volume of gas
that would be produced by combustion, either of the waste or the
subsequent combustion of the fuel in the generator. By cleaning the
pyrolysis product the volume of gas to be filtered and cleaned may
be lower than the volume of gas that would need to be filtered and
cleaned in a combustion exhaust; as a result smaller filters may be
used with associated advantages in terms of capital and operating
costs.
Preferably the process includes storing the waste in a vessel prior
to feeding the waste to the pyrolysis reactor, wherein the waste is
blended whilst stored in the vessel. It will be appreciated that
waste collected tends to vary in composition from hour to hour and
day to day. That may present a particular challenge when trying to
convert the waste into a desired product, as the composition of the
waste feed may affect the composition and attributes of the
product. Even if sophisticated control of the process to adjust
operating conditions to compensate for the variable composition of
the waste is available, it can still be advantageous to try to
minimise the variations in waste composition. By storing the waste
in a blended storage tank, variations in composition may be to some
extent averaged out. Even if such storage does not completely
eliminate variations, it may smooth the rate at which the
composition changes, and may therefore allow more time for the
control system to apply adjustments.
Preferably the waste is dried in a dryer prior to being fed to the
pyrolysis reactor. The dryer may reduce the water content of the
waste to less than 5 wt %, preferably less than 3 wt %. The dryer
may reduce the water content of the waste to between 2 and 3 wt %.
When the waste is fed to the pyrolysis reactor, it is heated to the
reaction temperature. Heating any water that is in the waste
requires extra energy and therefore it may be advantageous to
remove the water in a dryer before the waste is heated. If the fuel
is being stored as a liquid, any water in the waste is heated to
form steam in the reactor and then condensed again to water in the
condenser, resulting in a waste of energy.
Preferably the temperature in the pyrolysis reactor is controlled
so as to produce a fuel comprising C.sub.5 to C.sub.100
hydrocarbons. The mean chain length of the fuel, based on the
number of molecules, is preferably in the range C.sub.5 to
C.sub.40, more preferably in the range C.sub.10 to C.sub.20. It may
be that 80 wt % of the fuel consists of hydrocarbons with a chain
length in the range C.sub.5 to C.sub.40, more preferably in the
range C.sub.5 to C.sub.20, more preferably in the range C.sub.10 to
C.sub.20. Preferably the hydrocarbons in the fuel have a chain
length greater than C.sub.5. That may be achieved by passing the
fuel through a condenser and separating off the part of the fuel
that remains as a gas following the condensation (the gas
fraction). The liquid fraction may then be used as the fuel and the
gas fraction used elsewhere in the process or the host
facility.
For example, the fuel may be bunker fuel. It will be appreciated
that the composition of the fuel may be selected based on the
generator used in the process. The hydrocarbon chain length of the
fuel affects the heat of combustion of the fuel. Shorter chain
lengths result in a higher heat of combustion. However, at very
short chain lengths (for example, less than C.sub.5), a small
change in chain length can result in a large change in heat of
combustion. That can result in control challenges, as, for example,
a small decrease in the average chain length of the fuel can lead
to a large increase in the energy released when the fuel is
combusted and can therefore cause engine failures. Conversely, at
very long chain lengths (for example, greater than C.sub.40) a
large change in the average chain length may be required to produce
a significant change in heat of combustion. That may lead to
control challenges in that large control variations may be needed
to produce a noticeable effect on the fuel. The average chain
length of the fuel is therefore preferably selected so as to be at
a value where changes in the fuel chain length produce a sensible
change in the heat of combustion in the fuel. In that way control
variations can be used to alter the heat of combustion of the fuel
as necessary, but short-term deviations outside the control range
do not have catastrophic consequences.
As mentioned above, control of the process may be challenging due
to the variability of the waste fed to the process. The process may
be controlled by monitoring the waste input or by monitoring the
generator but the process is preferably controlled by monitoring an
attribute of the fuel and adjusting the temperature and/or the
residence time of the pyrolysis reactor in response to the measured
attribute of the fuel so as to maintain that attribute within a
desired range. It may be that the temperature of the reactor is
adjusted. It may be that the residence time of the reactor is
adjusted, for example by adjusting the flowrate through the
reactor. It may be that both the temperature and the residence time
of the reactor are adjusted. Preferably the attribute is related to
the heat of combustion, or the calorific value, of the fuel. For
example, the attribute may be the heat of combustion of the fuel or
it may be a parameter whose value is dependent on the heat of
combustion of the fuel. The attribute of the fuel could be measured
in the buffer tank, but is preferably measure at the inlet to the
tank so as to avoid the large volume of fuel in the tank slowing
the response time of the control system. By monitoring the fuel
entering the tank, the control system can detect variations in the
process more rapidly and apply any necessary adjustment. For
example, if the monitor detects that the heat of combustion of the
fuel entering the buffer tank is falling, the control system can
increase the heat of the reactor or increase the residence time in
the reactor. That may be achieved by feeding a greater quantity of
the fuel to the burners heating the reactor or by reducing the
flowrate through the reactor. Conversely, if the monitor detects
that the heat of combustion of the fuel is rising too high, the
temperature in the reactor can be decreased or the residence time
in the reactor can be decreased.
The heat of combustion of the fuel is preferably controlled using a
solvent monitor. Such a system may involve providing a hydrogen
flame, feeding a sample of the fuel into the flame and recording
the flame temperature. The heat of combustion of the flame may be
related to the difference between the flame temperature with the
fuel added and the temperature of the hydrogen flame but the
process may be controlled more straightforwardly by controlling the
process so as to achieve a flame temperature with the fuel added
within a desired range. For example, a thermocouple may be provided
to monitor the flame temperature and the output from the
thermocouple used as an input to the control process for the
reactor. Such a system may be a cheap and simple option for
monitoring the fuel quality. By monitoring the fuel quality the
response time of the control system may be improved. For example,
if the control system monitors the generator operation, by the time
a decrease in power is observed, a large quantity of sub-standard
fuel may already have been produced. That may be particularly the
case where the fuel is stored in a buffer tank. Furthermore, it may
be more straightforward to monitor the fuel quality, since the fuel
is a fluid, than it is to monitor the composition of the incoming
waste.
Heat of combustion is a well-known attribute and the skilled person
can measure the heat of combustion. For example, the heat of
combustion of solids may be measured using methods such as
ISO1928:2009 and the heat of combustion of liquid hydrocarbons may
be measured using methods such as ASTM D4809. It may be that the
heat of combustion of the waste is around 30 MJ/kg, for example in
the range 25 MJ/kg to 35 MJ/kg. Preferably the process is
controlled so as to produce a fuel having a heat of combustion less
than 45 MJ/kg. More preferably the process is controlled so as to
produce a fuel having a heat of combustion in the range 42 MJ/kg to
45 MJ/kg, even more preferably 44 MJ/kg to 45 MJ/kg. A fuel with a
heat of combustion in that range may be at a point on a curve of
heat of combustion against average chain length where controlled
variations in the heat of combustion can be achieved by varying the
temperature and/or residence time of the pyrolysis reactor so as to
vary the average chain length. Fuels below that range may be in a
region of the curve where undesirably large changes in reactor
conditions are needed to vary the heat of combustion and fuels
above that range may be in a region where unavoidable variations in
the reactor conditions result in undesirably large fluctuations in
the heat of combustion. Nevertheless, it may still be advantageous
to operate in the higher or lower regions in some circumstances.
For example, at lower heats of combustion the process may be very
stable and at higher heats of combustion more power may be
available.
The temperature in the reactor may, for example, be in the range
400.degree. C. to 600.degree. C. The reactor may be a fluidised bed
reactor, with the fluidised bed having a mass of 2.5 to 8 tonnes,
preferably 2.5 to 5 tonnes, more preferably 2.5 to 3.5 tonnes. The
reactor or the fluidised bed may have an aspect ratio
(height:width) of around 1:1, for example in the range 0.5:1 to
1:2, preferably in the range 0.8:1 to 1:1.2. Such a reactor size,
shape and temperature may allow efficient treatment of the
waste.
Preferably a product from the pyrolysis reactor is combusted to
heat a fluid, the fluid being used to heat the pyrolysis reactor.
The fluid may comprise the fuel. For example, a portion of the fuel
output stream from the pyrolysis reactor may be directed through a
heater, preferably an indirect heater, and back into the pyrolysis
reactor.
The product from the pyrolysis reactor may comprise the fuel. The
product from the pyrolysis reactor may comprise part of the fuel
output stream from the pyrolysis reactor that is not sent to the
generator. For example, if the process comprises passing the fuel
through a condenser to form a liquid fraction and a gas fraction
and using the liquid fraction of the fuel to run the generator, the
product combusted to heat the fluid used to heat the pyrolysis
reactor may comprise the gas fraction. It may be that the gas
fraction is sufficient to heat the pyrolysis reactor but it may be
that extra heat is needed, in which case it may be that the gas
fraction is supplemented by some of the liquid fraction. The gas
fraction is preferably supplemented by a stream of the fuel product
from the pyrolysis reactor that is taken from upstream of the
condenser. In that way energy is not wasted condensing the fuel
only to combust it again immediately to heat the reactor. It may be
that the gas fraction exceeds the amount of heat required to heat
the pyrolysis reactor. In such cases the excess gas may be used
elsewhere or flared.
It may be that the product from the pyrolysis reactor combusted to
heat the fluid that is used to heat the pyrolysis reactor is a
by-product of the pyrolysis. For example, the product may be char.
For example, the pyrolysis reactor may be a fluidised bed reactor
and the process may comprise removing a portion of the fluidised
bed that has become at least partially coated in char from the
reactor, separating the char, returning the portion of the
fluidised bed to the reactor and combusting the char to heat a
fluid that is used to heat the reactor. By combusting the char to
provide the heat, none of the fuel product is used for heating the
reactor so the process can provide more energy through the
generator.
By combusting part of the product to provide heat, the process does
not require a separate fuel source for normal operation. The
skilled person will appreciate that for start-up a separate source
of heat may still be required. By using combustion of the product
to heat a further stream comprising the fuel, with the further
stream being introduced into the pyrolysis reactor, the combustion
products may be kept out of the reactor. Such an indirect heating
system may allow combustion to provide heat, without the reactor
becoming contaminated with combustion products.
Preferably the fuel is used to run a first generator and a second
generator. For example, the first generator may be run continuously
and the second generator run intermittently according to grid
demand. It may be that the first generator is smaller than the
second generator. It may be that the first generator is larger than
the second generator. For example, the first generator may be used
to provide continuous power to the host facility in which the
process operates and the second generator could be used to produce
power to sell to the grid. Preferably the first generator is sized
according to the heat or electricity demand of the host facility.
Preferably the second generator has a short start-up cycle, for
example starting up in less than 10 minutes, so as to be able to
provide reserve power to the grid at short notice. The ability to
act as part of the grid's reserve may be advantageous in terms of
the prices that the grid will pay. It may be that the first
generator forms part of a control system, with the generator's
performance being monitored and the measured performance being used
to control the operating conditions, for example the temperature
and residence time of the pyrolysis reactor, of the process.
The generators may, for example, be turbines, preferably gas
turbines, but are preferably internal combustion engines attached
to generators. For example, the engine may be a marine diesel
engine, which may, for example, run on bunker fuel. In such a case,
the control system could be calibrated so as to produce bunker fuel
in the buffer tank. Combining the use of bunker fuel in a marine
diesel with a step of filtering the fuel before it is used in the
marine diesel can be advantageous as the cleaned fuel may mean that
the emissions from the marine diesel engine are reduced. That may
be particularly advantageous, as bunker fuel may be considered to
be highly polluting and therefore require expensive exhaust
clean-up unless the filtering is used.
Preferably the process treats from 5,000 to 20,000 tonnes per year
of waste, more preferably 5,000 to 10,000 tonnes per year of waste
and even more preferably 6,000 to 8,000 tonnes per year of waste.
For example it may be that the process treats 7,000 tonnes per year
of waste. Processes of those sizes can be conveniently combined
with existing recycling facilities so as to treat Mixed Plastic
Waste on-site, rather than having to transport the waste to
another, larger facility such as a power station. Transporting
waste uses energy and may therefore reduce or eliminate the
environmental benefit of subsequent treatment. Preferably the
process produces from 1.8 to 10 MW, more preferably 1.8 to 5 MW and
even more preferably 2.1 to 4 MW. For example, it may be that the
process produces from 2.5 to 3.5 MW of electricity.
Preferably the process includes cooling the exhaust from the
generator by heat exchange with an air stream, wherein at least
part of the air stream is used to provide heat elsewhere in the
process or elsewhere in the host facility in which the process is
carried out. For example, the air stream may be used to provide
heat in the dryer, thus improving the overall efficiency of the
process.
The generator may be cooled by heat exchange, for example indirect
heat exchange with a fluid stream and at least part of that fluid
stream may then be used to provide heat to another part of the
process, for example the dryer, or to another process in the host
facility. Preferably the generator is cooled by heat exchange with
a water stream, wherein at least part of the water stream is used
to provide heat elsewhere in the process or elsewhere in the host
facility.
Preferably the pyrolysis reactor is a fluidised bed reactor. For
example, the pyrolysis reactor may contain a fluidised bed of
particles, such as sand, and a distributor for feeding a
fluidisation medium into the reactor. The fluidisation medium may,
for example, be recycled pyrolysis product, which may have been
heated in order to supply energy to the pyrolysis reactor. The
distributor design may be an important part of the fluidised bed
design so as to achieve a uniform distribution of the fluidising
medium across the bed. Moreover, the fluidised bed may accumulate
contaminants over time and the particles of the bed, for example
sand, may need cleaning. For example, tar, char or coke may
accumulate on the particles. The cleaning could be achieved by
shutting down the reactor and removing the particles, but it is
advantageously performed on-line by a recirculation of the
particles through a cleaning system. The distributor is preferably
configured so as to allow a portion of the fluidised particles to
fall through the distributor and the process preferably comprises
removing a portion of the particles that have fallen through the
distributor, cleaning the particles and feeding the particles back
into the reactor. In that way a continuous recirculation of the
particles through the cleaning apparatus may be achieved. For
example, the distributor may comprise an array of ducts with
orifices, for example in their surface, the ducts being configured
such that the fluidising medium is fed to the ducts and exits the
ducts through the orifices into the reactor, wherein the array of
ducts is configured such that the particles can fall between the
ducts. The ducts may for example be arranged in a row or a grid,
with the spacing between the ducts being selected so as to allow
the particles to pass between the ducts. It will be appreciated
that steps may be taken to prevent the particles that are falling
from the fluidised bed falling into, and blocking, the orifices.
The orifices may, for example, be in the underside of the ducts. In
another example, the orifices may comprise a nozzle comprising a
cap to prevent particles blocking the orifice.
It will be appreciated that using the heat from the generator may
provide significant advantages in terms of efficiency. As well as
providing electrical power to the host facility, the generator can
also supply heat to the host facility. Such a `combined heat and
power` approach allows the energy in the fuel to be efficiently
transformed into useful energy for the host facility. Thus, in a
broad aspect of the invention there is provided a process for
treating waste comprising Mixed Plastic Waste at a host facility,
the process comprising: providing an apparatus comprising a
pyrolysis reactor and a generator at the host facility; feeding the
waste to a pyrolysis reactor; pyrolysing the waste in the pyrolysis
reactor to produce a fuel; and using the fuel to run a generator to
produce energy.
It may be that the energy is electrical energy; that is the
generator is run to produce electricity. It may be that the energy
is heat energy. Preferably the energy is both electrical and heat
energy. Such a `combined heat and power` approach may be
advantageous because the generator may require cooling even if
being run to produce electricity and it may therefore be
advantageous to make use of the heat energy as well. The host
facility may be a site having energy demands. Preferably the energy
is used within the host facility. For example, the host facility
may be a recycling plant and the energy may be used in other parts
of the recycling process.
It will be appreciated that controlling the process is an inventive
feature of the process in its own right and may be particularly
important when there is significant variability in the waste feed.
Thus, in a second aspect of the invention there is provided a
process for treating waste comprising Mixed Plastic Waste, the
process comprising: feeding the waste to a pyrolysis reactor;
pyrolysing the waste in the pyrolysis reactor to produce a fuel;
monitoring an attribute of the fuel; and adjusting the temperature
and/or residence time of the pyrolysis reactor in response to the
measured attribute of the fuel so as to maintain the attribute
within a desired range.
Preferably the attribute is related to the heat of combustion of
the fuel.
The design of the distributor is an inventive feature of the
process in its own right. Thus, in a third aspect of the invention
there is provided a process for treating waste comprising Mixed
Plastic Waste, the process comprising: feeding the waste to a
pyrolysis reactor, the pyrolysis reactor being a fluidised bed
reactor; and pyrolysing the waste in the pyrolysis reactor to
produce a fuel; wherein the pyrolysis reactor contains a fluidised
bed of particles and a distributor for feeding a fluidisation
medium into the reactor, wherein the distributor is configured such
that the particles can fall through the distributor and wherein the
process comprises removing a portion of the particles that have
fallen through the distributor, cleaning the particles and feeding
the particles back into the reactor.
Heating the pyrolysis reactor is an inventive feature of the
process in its own right. Thus, according to a fourth aspect of the
invention there is provided a process for treating waste comprising
Mixed Plastic Waste, the process comprising: feeding the waste to a
pyrolysis reactor, for example a fluidised bed reactor; and
pyrolysing the waste in the pyrolysis reactor to produce a fuel;
and combusting a product from the pyrolysis reactor to heat a
fluid, and feeding the fluid into the pyrolysis reactor so as to
heat the pyrolysis reactor.
It may be that the product is a by-product, for example char. It
may be that the product comprises the fuel. It may be that the
product comprises a part of the fuel output stream from the
pyrolysis reactor that is not used to run the generator.
The processes of the above aspects of the invention are
particularly suited to use in small to moderate sized recycling
facilities, where they complement the facilities already present.
For example, the electricity and heat generated by the process of
the above aspects of the invention can be used to power recycling
operations at the centre. Thus, according to a fifth aspect of the
invention there is provided a process for recycling waste material,
the process comprising a process for treating waste comprising
Mixed Plastic Waste according to any of the above aspects of the
invention.
It will be appreciated that the process of the invention is carried
out at a site, or host facility, for example a recycling or waste
processing facility. According to a sixth aspect of the invention
there is provided an apparatus for treating waste comprising Mixed
Plastic Waste, the apparatus comprising: a pyrolysis reactor for
pyrolysing the waste to produce a fuel; and a generator configured
to run on the fuel to produce electricity.
Preferably the apparatus comprises a condenser downstream of the
pyrolysis reactor and upstream of the generator for condensing the
fuel prior to using it to run the generator.
Preferably the apparatus comprises a buffer tank downstream of the
pyrolysis reactor and upstream of the generator for storing the
fuel prior to using it to run the generator.
Preferably the apparatus comprises a filter system downstream of
the pyrolysis reactor and upstream of the generator for filtering
the fuel to remove chemical contaminants.
Preferably the apparatus includes a storage vessel upstream of the
pyrolysis reactor for storing the waste prior to feeding the waste
to the pyrolysis reactor, wherein the storage vessel comprises a
blending system for blending the waste stored in the vessel.
Preferably the apparatus comprises a dryer upstream of the
pyrolysis reactor for drying the waste.
Preferably the apparatus comprises: a monitor, preferably a solvent
monitor, for monitoring an attribute of the fuel; and a controller
for adjusting the temperature and/or residence time of the
pyrolysis reactor in response to the measured attribute of the fuel
so as to maintain the attribute within a desired range. Preferably
the attribute is related to the heat of combustion of the fuel.
Preferably the apparatus comprises a combustor to combust a product
from the pyrolysis reactor to heat a fluid that is fed into the
pyrolysis reactor to heat the pyrolysis reactor. It may be that the
product is a by-product, for example char. It may be that the
product comprises the fuel. It may be that the product comprises a
part of the fuel output stream from the pyrolysis reactor that is
not used to run the generator.
Preferably the generator comprises an internal combustion engine,
for example a marine diesel engine.
Preferably the apparatus is sized and configured to treat from
5,000 to 20,000 tonnes per year of waste, more preferably 5,000 to
10,000 tonnes per year of waste and even more preferably 6,000 to
8,000 tonnes per year of waste.
Preferably the apparatus is sized and configured to produce from
1.8 to 10 MW, more preferably 1.8 to 5 MW and even more preferably
2.1 to 4 MW. For example, it may be that the process produces from
2.5 to 3.5 MW of electricity.
Preferably the pyrolysis reactor is a fluidised bed reactor.
Preferably the pyrolysis reactor is configured to contain a
fluidised bed of particles and the apparatus comprises a
distributor for feeding a fluidisation medium into the reactor,
wherein the distributor is configured such that the particles can
fall through the distributor and wherein the pyrolysis reactor
includes an outlet, such as a rotary valve, through which, in use,
a portion of the particles that have fallen through the distributor
can be removed, an apparatus for cleaning the particles and an
inlet through which the cleaned particles can be fed back into the
reactor. The inlet is preferably above the distributor in the
fluidised bed reactor.
Preferably the distributor comprises an array of ducts with
orifices in their surface, wherein the ducts in the array are
spaced apart such that, in use, the particles can fall between the
ducts.
According to a seventh aspect of the invention there is provided an
apparatus for treating waste comprising Mixed Plastic Waste, the
apparatus comprising: a pyrolysis reactor for pyrolysing the waste
to produce a fuel; a monitor for monitoring an attribute of the
fuel; and a controller for adjusting the temperature and/or
residence time of the pyrolysis reactor in response to the measured
attribute of the fuel so as to maintain the attribute within a
desired range.
Preferably the attribute is related to the heat of combustion of
the fuel.
According to an eighth aspect of the invention there is provided an
apparatus for treating waste comprising Mixed Plastic Waste, the
apparatus comprising: a pyrolysis reactor for pyrolysing the waste
to produce a fuel, the pyrolysis reactor being a fluidised bed
reactor; wherein the pyrolysis reactor is configured to contain a
fluidised bed of particles and wherein the apparatus comprises a
distributor for feeding a fluidisation medium into the reactor,
wherein the distributor is configured such that the particles can
fall through the distributor and wherein the pyrolysis reactor
includes an outlet through which, in use, a portion of the
particles that have fallen through the distributor can be removed,
an apparatus for cleaning the particles and an inlet through which
the cleaned particles can be fed back into the reactor.
According to a ninth aspect of the invention there is provided an
apparatus for treating waste comprising Mixed Plastic Waste, the
apparatus comprising: a pyrolysis reactor for pyrolysing the waste
to produce a fuel, for example a fluidised bed reactor; and a
combustor to combust a product from the pyrolysis reactor to heat a
fluid that is fed into the pyrolysis reactor to heat the pyrolysis
reactor.
It may be that the product is a by-product, for example char. It
may be that the product comprises the fuel. It may be that the
product comprises a part of the fuel output stream from the
pyrolysis reactor that is not used to run the generator.
Advantageously the apparatus is portable in that it is constructed
in such a way that it can be broken down into a number of modules,
each of which is transportable. For example elements of the
apparatus may be individually mounted in frames compatible with the
ISO standards for freight containers to create modules that can be
individually transported using equipment designed for the handling
of freight containers. The modules may be made at a factory
facility and then shipped to the location in which they are to be
used, where they are connected together with other modules to form
the apparatus. That may be a cost effective system of providing the
apparatus at the location and may reduce the need for skilled
labour at the location to install the apparatus. In some examples,
the apparatus may be employed at a first location to treat a volume
of waste stored at the first location, before being dismantled and
transported to a second location to treat a volume of waste stored
at that second location. In that way, a number of small waste
collection facilities may be serviced on a rotational basis, rather
than shipping the waste to a central location. In some examples the
apparatus may be mounted in a portable manner, for example on a
ship, so that the apparatus can be operated whilst the ship is in
motion. Advantageously such an apparatus could be used to treat
large islands of plastic waste that accumulate in the oceans.
According to a tenth aspect of the invention there is therefore
provided an apparatus for treating waste comprising Mixed Plastic
Waste, the apparatus comprising: a pyrolysis reactor for pyrolysing
the waste to produce a fuel, for example a fluidised bed reactor;
wherein the pyrolysis reactor is mounted in a frame having fittings
that are compatible with the load handling equipment used to
transport freight containers.
The frame may be part of a freight container; that is, the reactor
may be mounted in a freight container, but preferably the frame is
an open frame, in that the module has the shape of a freight
container and comprises structural members along the module edges
but does not include panelling to close the faces of the module.
Such a frame may be lighter and allow better access to the
equipment.
Preferably the apparatus comprises a generator configured to run on
the fuel to produce electricity; wherein the generator is mounted
in a frame having fittings that are compatible with the load
handling equipment used to transport freight containers.
Preferably the apparatus comprises a buffer tank downstream of the
pyrolysis reactor and upstream of the generator for storing the
fuel prior to using it to run the generator; wherein the buffer
tank is mounted in a frame having fittings that are compatible with
the load handling equipment used to transport freight
containers.
The apparatus may comprise further elements, for example: filters,
dryers or storage tanks with blending systems, as described above
in relation to aspects one to nine of the invention. Some or all of
those elements may also be mounted in frames having fittings that
are compatible with the load handling equipment used to transport
freight containers. It may be that, in some frames, more than one
element is mounted. Such an arrangement may be advantageous in
reducing the number of frames that need transporting. It may be
that each element is mounted in a separate frame. Such an
arrangement may be advantageous in allowing exchangeability of
components.
According to an eleventh aspect of the invention there is provided
a recycling plant for recycling waste material, the plant
comprising an apparatus for treating waste comprising Mixed Plastic
Waste according to any of the above aspects of the invention.
Preferably the recycling plant is sized to process from 5,000 to
100,000 tonnes of waste material per year. As such the recycling
plant may be an existing facility serving a city or a group of
towns and the apparatus may be installed at the plant to provide a
process for treating Mixed Plastic Waste, which otherwise would
have been sent away from the plant to be treated or landfilled
elsewhere.
It will of course be appreciated that features described in
relation to one aspect of the present invention may be incorporated
into other aspects of the present invention. For example, the
apparatus of the invention may incorporate any of the features
described with reference to the process of the invention and vice
versa. Similarly any process or apparatus aspect of the invention
may incorporate any of the features described with reference to
other process or apparatus aspects of the invention.
DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described by way
of example only with reference to the accompanying schematic
drawings of which:
FIG. 1 is a schematic view of an apparatus according to a first
embodiment of the invention;
FIG. 2 is a schematic view of a distributor in the pyrolysis
reactor of FIG. 1; and
FIG. 3 is a schematic view of a control system for the apparatus of
FIG. 1.
DETAILED DESCRIPTION
In FIG. 1 an apparatus 1 for treating waste comprising Mixed
Plastic Waste has a loading conveyer 3. The loading conveyer 3
feeds a de-water press 5, the outlet of which is arranged above a
conveyer 7 to a shredder 9. The outlet of the shredder 9 is
directed at a conveyer 11 to a filter 13, which includes a ferrous
and non-ferrous filter. The outlet of the filter 13 is connected to
a dryer 15 and the outlet of the dryer 15 is connected to a storage
tank 17. The storage tank 17 is fed by conveyer 19 and comprises a
blending system. The outlet of storage tank 17 is connected via
line 21 to the inlet of a fluidised bed pyrolysis reactor 23. The
reactor 23 contains sand, which forms the fluidised bed. The bottom
of the reactor 23 has a valve connected, via line 25, to a cleaner
27, which in turn is connected, via line 29 to a hopper 31. The
hopper 31 feeds into the reactor 23. The outlet from the top of the
reactor 23 is connected to hot gas filter 33, the outlet of which
is connected, via line 35, to condenser 37.
From line 35, a branch 39 is connected, via pump 41, to heat
exchanger 43. From heat exchanger 43 a line 45 feeds into reactor
23. Fuel supply line 49 runs from line 35 to burner 53. Fuel supply
line 47 runs from the top of condenser 37 to burner 51. Burners 51
and 53 are mounted on heat exchanger 43.
Condenser 37 is on top of, and feeds into, buffer tank 55. An
outlet 57 from the buffer tank 55 is connected, via pump 59, to
engine 61, which is attached to generator 63. Engine 61 and
generator 63 together form a generator to produce electricity and
heat. Cooling water loop 65 runs through engine 61 and heat
exchanger 67. Water line 69 passes through heat exchanger 67 and on
to another part of the plant. The exhaust 71 from the engine 61
passes through heat exchanger 73 and then filter 75 before being
exhausted to the atmosphere. Air line 77 passes through heat
exchanger 73 and on to another part of the plant.
In FIG. 2, the lower part of the reactor 23 has a distributor 79.
The distributor 79 is at the bottom of the fluidised bed 85. The
distributor 79 comprises an array of ducts 81a-e with orifices
89a-e in their upper surface. The orifices comprise nozzles 83a-e,
which sit on top of the orifices. The ducts 81a-e are spaced apart
such that the gaps between the ducts are large enough for particles
from the fluidised bed 85 to fall through. At the bottom of the
reactor 23 there is a valve 87 leading to line 25.
In FIG. 3 a solvent monitor 91 is mounted on line 35. The solvent
monitor 91 is in communication with reactor management system 93.
Temperature monitor 99 is in reactor 23 and is also in
communication with reactor management system 93. Reactor management
system 93 is in communication with gas burner control 95, which
controls burners 51 and 53, and material feed control 97, which
controls the feed rate from line 21 into reactor 23.
In use, 7000 tonnes per year of waste, in this embodiment Mixed
Plastic Waste, is loaded continuously onto the loading conveyer 3.
The waste travels up the loading conveyer 3 and drops into the
de-water press 5, where the pressing action forces water out of the
waste. The dried waste, which has a moisture content of about 15%
by weight exits the de-water press 5 and is conveyed along conveyer
7 and into the shredder 9, where it is shredded. The shredded waste
exits shredder 9 and travels along conveyer 11 to filter 13. Filter
13 comprises ferrous and non-ferrous filters and removes metallic
contaminants from the waste. The de-watered, shredded and filtered
waste then passes into dryer 15, where the water content is reduced
to about 2-3 wt %. The dryer 15 is powered by heat from hot water
line 69 or hot air line 77, or both. On exiting the dryer 15, the
dry, shredded, filtered waste is stored in storage tank 17. Whilst
in the storage tank 17, the waste is constantly blended by
withdrawing a portion of the waste from the bottom of one end of
storage tank 17 and recirculating it to conveyer 19 to be
redistributed across the top of storage tank 17. With waste also
being continuously added to and withdrawn from storage tank 17 to
feed the process, the effect of the blending recirculation is to
smooth variations in the composition of the waste over time.
Waste is withdrawn from the storage tank 17 along line 21 and fed
to the fluidised bed pyrolysis reactor 23. On entering the reactor
23, the waste is heated to around 400 to 600.degree. C. The heating
is achieved by feeding a hot stream into the reactor 23 along line
45. That hot stream comprises pyrolysis product drawn from line 35,
along line 39, and heated indirectly by combustion of a portion of
the pyrolysis product, which is also drawn from line 35, along line
47 or 49. The portion of the pyrolysis product combusted is
normally drawn along line 47 from the top of the condenser 37 and
comprises the gas fraction of the fuel output stream 35 from the
pyrolysis reactor 23 that does not condense in the condenser 37.
When extra fuel is required, it is drawn directly from the fuel
output stream in line 35 along line 49. In that case, some of the
fuel product that would in normal circumstances be used to run the
engine 61 is being used to heat the pyrolysis reactor 23.
The heated waste undergoes a pyrolysis reaction that decreases the
hydrocarbon chain lengths to around C.sub.5 to C.sub.100. The
process is carried out in a fluidised bed 85 of sand, which results
in good mixing and even temperature across the reactor 23. The sand
becomes contaminated with by-products over time. To prevent
excessive build-up, a portion of the sand is continuously withdrawn
from the bottom of reactor 23 along line 25 and cleaned in cleaner
27. The cleaned sand is reheated and fed back into the reactor 23
via line 29 and hopper 31.
The products of the pyrolysis reaction exit the top of the reactor
23 and pass through hot gas filter 33. The filter 33 removes
chemical contaminants such as chlorides (resulting from PVC in the
Mixed Plastic Waste) and sulphates, resulting in a clean fuel gas
which flows along line 35 and is condensed into buffer tank 55 by
condenser 37.
The quality of the fuel in line 35 is monitored continuously by
solvent monitor 91. Solvent monitor 91 measures a flame temperature
resulting from burning a sample of the fuel in a hydrogen flame.
The temperature of the flame can be related to the heat of
combustion of the fuel. Solvent monitor 91 communicates the flame
temperature to reactor management system 93 by means of an
electronic signal from a thermocouple in solvent monitor 91.
Reactor management system 93 also receives a signal from
temperature monitor 99 in the pyrolysis reactor 23. Reactor
management system 93 responds to changes in the flame temperature
of solvent monitor 91 by adjusting the operation of burners 51 and
53 and the feed rate from line 21 into pyrolysis reactor 23 by
means of gas burner control 95 and material feed control 97. In
that way, reactor management system 93 can adjust the temperature
and/or the residence time of the pyrolysis reactor 23. Thus, if
solvent monitor 91 detects that the flame temperature is falling,
indicating that the quality of the fuel is falling, the reactor
management system 93 increases the temperature in the reactor 23,
or increases the residence time in the reactor 23, or both. The
average chain length of the fuel in the output from the reactor 23
should then decrease and the quality of the fuel increase.
Conversely, if the solvent monitor 91 indicates that the heat of
combustion of the fuel is rising, which could cause problems in
engine 61, the reactor management system 93 can reduce the
temperature or residence time or both of the reactor 23 so as to
decrease the pyrolysis of the waste and maintain the flame
temperature of the solvent monitor 91 within its desired range.
The level of fuel in buffer tank 55 can be allowed to increase and
decrease. Thus the reactor 23 can be run continuously at a constant
steady state, but the fuel can be used in a discontinuous way or at
a varying rate. At night, when the demand for electricity is low,
the level of fuel in the buffer tank 55 rises, whilst at times of
peak demand the level of fuel in the buffer tank 55 can be allowed
to decrease.
The fuel in buffer tank 55 is continuously recirculated so as to
mix the fuel and smooth temporal variations in the quality of the
fuel entering the tank 55 from condenser 37. The recirculation also
helps to smooth spikes in contaminant concentrations that could
otherwise lead to undesirable short term emissions levels.
The fuel from buffer tank 55 is used to run engine 61, which is
connected to generator 63. Together, engine 61 and generator 63
form a generator that is run on the fuel to produce electricity.
Engine 61 is a marine diesel engine designed to run on bunker fuel
and the temperature in reactor 23 is controlled by monitoring the
fuel entering condenser 37 so as to achieve the correct fuel
specifications for engine 61. By combining the fuel generation
process with the electricity generation in a single process, the
fuel specification can be relaxed. Engine 61 can be selected based
in part on its ability to handle fuel of varying specification with
the result that the acceptable specification for the fuel in buffer
tank 55 can be broader than if the fuel was to be sold as
commercial fuel.
The engine 61 requires cooling and generates hot exhaust gases. The
heat from those streams can be captured and used elsewhere in the
host facility. In this embodiment, the heat is used in dryer 15 and
also in other processes in the host facility. Thus the process
provides combined heat and power to the facility. Cooling water
circulates through the engine in cooling water line 65. The cooling
water cools the engine 61, and is heated in that process. The
cooling water then passes to heat exchanger 67, where it is cooled
by indirect contact with cool water entering heat exchanger 67
along line 69. The cooled cooling water exits heat exchanger 67 and
returns to the engine 61 to repeat the cycle. The water heated in
the heat exchanger 67 exits along line 69 and is used to provide
heat to the dryer 15 and also to other processes in the host
facility. The hot exhaust from the engine 61 is cooled by indirect
contact with an air stream in heat exchanger 73. The exhaust gases
exit the engine 61 along exhaust line 71 and pass through the heat
exchanger 73. Air stream 77 also passes through heat exchanger 73
and heat is passed from the exhaust to the air stream. The exhaust
gases then continue along exhaust line 71, through filter 75 to
remove contaminants and particulates and are vented to the
atmosphere. The air stream 77 that has been heated in heat
exchanger 73 is directed to the dryer 15, where the heat in the
stream is used to dry the incoming waste, and also to other
processes in the host facility that use heat.
Whilst the present invention has been described and illustrated
with reference to particular embodiments, it will be appreciated by
those of ordinary skill in the art that the invention lends itself
to many different variations not specifically illustrated herein.
By way of example only, certain possible variations will now be
described.
Engine 61 and generator 63 may be replaced by other generator
systems. For example, in some embodiments a turbine may be used. In
some embodiments two generators are provided. A small generator
runs continuously to provide a base level of electrical power to
run the remainder of the recycling facility in which the apparatus
is installed. A large generator is turned on when the national
electricity grid requires short-term supplies of electricity. The
large generator is selected so as to have a quick start-up cycle so
as to benefit from the higher price that national grids are willing
to pay for electrical generating capacity that is available at
short notice.
In some embodiments the de-watering press 5, shredder 9 and filter
13 are provided in a different order. In some embodiments the waste
may be shredded first and then de-watered and filtered. In other
embodiments the three steps may be performed in other orders.
In some embodiments the de-watering press 5 is replaced by another
de-watering system such as a de-watering centrifuge.
In some embodiments, the fuel gas that is heated to be fed back
into the reactor 23 via line 45 in order to heat the incoming waste
is drawn from upstream of the hot gas filter 33. The volume of gas
passing through the hot gas filter 33 in such embodiments is
reduced as a result.
In some embodiments the waste fed to the process comprises Mixed
Plastic Waste, but also comprises organic material. In some
embodiments the waste is Municipal Solid Waste.
In some embodiments the fuel burners 51 and 53 are replaced or
supplemented by burners designed to burn the char separated from
the fluidised bed sand in cleaner 27. In that way the char
by-product of the pyrolysis process is used to heat the reactor
23.
In some embodiments the buffer tank is a plurality of intermodal
"20 ft" tank containers. In an example process, 1 tonne (1000 kg)
per hour of waste may be fed to the process and 850 kg per hour of
fuel produced by the reactor. A single "20 ft" tank container
provides enough storage for around 24 hours of operations with the
generator off, for example if the generator is undergoing
maintenance.
In another example embodiment the fluidised bed reactor has a 1.5 m
diameter and a 1:1 aspect ratio (diameter to height ratio). The
reactor contains 3 tonnes of sand.
Where in the foregoing description, integers or elements are
mentioned which have known, obvious or foreseeable equivalents,
then such equivalents are herein incorporated as if individually
set forth. Reference should be made to the claims for determining
the true scope of the present invention, which should be construed
so as to encompass any such equivalents. It will also be
appreciated by the reader that integers or features of the
invention that are described as preferable, advantageous,
convenient or the like are optional and do not limit the scope of
the independent claims. Moreover, it is to be understood that such
optional integers or features, whilst of possible benefit in some
embodiments of the invention, may not be desirable, and may
therefore be absent, in other embodiments.
* * * * *
References